1: #include <petsc/private/tsimpl.h> /*I "petscts.h" I*/

  3: typedef struct {
  4:   PetscReal safety;         /* safety factor relative to target CFL constraint */
  5:   PetscBool always_accept;
  6: } TSAdapt_CFL;

 10: static PetscErrorCode TSAdaptChoose_CFL(TSAdapt adapt,TS ts,PetscReal h,PetscInt *next_sc,PetscReal *next_h,PetscBool *accept,PetscReal *wlte)
 11: {
 12:   TSAdapt_CFL     *cfl = (TSAdapt_CFL*)adapt->data;
 13:   PetscErrorCode  ierr;
 14:   PetscReal       hcfl,cfltimestep,ccfl;
 15:   PetscInt        ncandidates;
 16:   const PetscReal *ccflarray;

 19:   TSGetCFLTime(ts,&cfltimestep);
 20:   TSAdaptCandidatesGet(adapt,&ncandidates,NULL,NULL,&ccflarray,NULL);
 21:   ccfl = (ncandidates > 0) ? ccflarray[0] : 1.0;

 23:   /* Determine whether the step is accepted of rejected */
 24:   *accept = PETSC_TRUE;
 25:   if (h > cfltimestep * ccfl) {
 26:     if (cfl->always_accept) {
 27:       PetscInfo3(adapt,"Step length %g with scheme of CFL coefficient %g did not satisfy user-provided CFL constraint %g, proceeding anyway\n",(double)h,(double)ccfl,(double)cfltimestep);
 28:     } else {
 29:       PetscInfo3(adapt,"Step length %g with scheme of CFL coefficient %g did not satisfy user-provided CFL constraint %g, step REJECTED\n",(double)h,(double)ccfl,(double)cfltimestep);
 30:       *accept  = PETSC_FALSE;
 31:     }
 32:   }

 34:   /* The optimal new step based purely on CFL constraint for this step. */
 35:   hcfl = cfl->safety * cfltimestep * ccfl;
 36:   if (hcfl < adapt->dt_min) {
 37:     PetscInfo4(adapt,"Cannot satisfy CFL constraint %g (with %g safety) at minimum time step %g with method coefficient %g, proceding anyway\n",(double)cfltimestep,(double)cfl->safety,(double)adapt->dt_min,(double)ccfl);
 38:   }

 40:   *next_sc = 0;
 41:   *next_h  = PetscClipInterval(hcfl,adapt->dt_min,adapt->dt_max);
 42:   *wlte    = -1;  /* Weighted local truncation error was not evaluated */
 43:   return(0);
 44: }

 48: static PetscErrorCode TSAdaptDestroy_CFL(TSAdapt adapt)
 49: {

 53:   PetscFree(adapt->data);
 54:   return(0);
 55: }

 59: static PetscErrorCode TSAdaptSetFromOptions_CFL(PetscOptionItems *PetscOptionsObject,TSAdapt adapt)
 60: {
 61:   TSAdapt_CFL    *cfl = (TSAdapt_CFL*)adapt->data;

 65:   PetscOptionsHead(PetscOptionsObject,"CFL adaptive controller options");
 66:   PetscOptionsReal("-ts_adapt_cfl_safety","Safety factor relative to target CFL constraint","",cfl->safety,&cfl->safety,NULL);
 67:   PetscOptionsBool("-ts_adapt_cfl_always_accept","Always accept the step regardless of whether CFL constraint meets goal","",cfl->always_accept,&cfl->always_accept,NULL);
 68:   /* The TS implementations do not currently communicate CFL information to the controller.  There is a placeholder, but
 69:    * we do not believe it to provide sufficiently rich information.  That means the CFL adaptor is incomplete and
 70:    * unusable.  Do not delete the guard below unless you have finished the implementation. */
 71:   if (!cfl->always_accept) SETERRQ(PetscObjectComm((PetscObject)adapt),PETSC_ERR_SUP,"Step rejection not implemented. The CFL implementation is incomplete/unusable");
 72:   PetscOptionsTail();
 73:   return(0);
 74: }

 78: /*MC
 79:    TSADAPTCFL - CFL adaptive controller for time stepping

 81:    Level: intermediate

 83: .seealso: TS, TSAdapt, TSSetAdapt()
 84: M*/
 85: PETSC_EXTERN PetscErrorCode TSAdaptCreate_CFL(TSAdapt adapt)
 86: {
 88:   TSAdapt_CFL    *a;

 91:   PetscNewLog(adapt,&a);
 92:   adapt->data = (void*)a;

 94:   adapt->ops->choose         = TSAdaptChoose_CFL;
 95:   adapt->ops->setfromoptions = TSAdaptSetFromOptions_CFL;
 96:   adapt->ops->destroy        = TSAdaptDestroy_CFL;

 98:   a->safety        = 0.9;
 99:   a->always_accept = PETSC_FALSE;
100:   return(0);
101: }